Stator Blades of an Axial Turbocompressor and Manufacturing Process

ABSTRACT

The present application relates to a stator of an axial turbomachine compressor having an external shell with a row of openings and an internal annular groove designed to hold an annular layer of abradable material forming a strip. The stator further includes a row of stator blades adjacent to the row of openings. The stator blades include platforms with surfaces matching the openings, the said platforms being fitted in the openings so as to mask them. Weld beads fix the platforms at their junctions with the openings. On one side of the row of stator blades a portion of the weld bead is situated axially in the internal annular groove. The present application also relates to methods of manufacturing the stator.

This application claims priority under 35 U.S.C. §119 to European PatentApplication No. 12193700.7, filed 21 Nov. 2012, which is incorporatedherein by reference for all purposes.

BACKGROUND

1. Field of the Application

The present application relates to the stator of an axial turbomachine.The present application also relates to an axial turbomachine comprisinga compressor and a turbine fitted with stators. The present applicationalso relates to a manufacturing process of an axial turbomachine stator.

2. Description of Related Art

In order to achieve a high compression ratio, an axial turbomachinecompressor commonly has several stages. A stage essentially consists ofa row of rotor blades followed by a row of stator blades. The cumulativelengths of these stages dictate the length of the compressor.

Patent FR 2404102 A1 discloses a fixed ring of blades of an axialturbomachine. The ring has an external shell having openings arranged inan annular row. The blades include external platforms which are weldedin the openings of the external shell. The external shell comprises anannular cavity filled with abradable material, the said cavity beinglocated close to the apertures and platforms. The cross section of theshell thus has a section of variable thickness close to the weldedsection between the shell and the platforms. The variable thickness ofmaterial in the vicinity of the weld bead generates an inhomogeneitywhich can cause problems in carrying out the welding.

Patent FR 2958323 A discloses a low pressure compressor of aturbomachine comprising several bladed stator stages. A stator stage hasan external shell in which aligned openings are formed. The blades haveplatforms which mate with the contours of the internal edges of theopenings in the external shell. A weld at their junction is used to fixthe blades through their platforms to the external shell. The size ofthe platforms ensures the bodies of the blades are not exposed duringthe welding operation.

However, to achieve optimum fixing by the welds, spatial and geometricconstraints must be observed. Among other things, the weld must bearranged to be in a homogeneous medium. This may result in the weldinghaving to be carried out away from bends and preferably through partshaving constant thicknesses. To overcome these constraints, the curvedregion must be distanced from the blades, which leads to a lengtheningof the blade platforms, and thus of the compressor.

In the context of a turbomachine, the low-pressure compressor occupiesmuch of the space. Extending it has an impact on the size and design ofthe turbomachine housing. The weight of the latter is increased. Whensuch a turbomachine is used as a means of propelling an aeroplane, theonboard weight is increased, as is that of the equipment needed for itssupport. The primary energy requirements and the wing surface area mustbe modified.

Patent EP 2202388 A1 discloses a turbomachine stator assembled withoverlap. Two cylindrical portions of the stator flanges overlap at thestator blades. This method of assembly is based on fixing using blindbolts. Although reducing the axial length, this solution increases theradial diameter. Moreover, this solution is not suitable for welding asvisual inspection of both sides of the weld is not possible. Thisconfiguration does not lend itself to electron beam welding due to thepresence of the blade in the weld.

Although great strides have been made in the area of stators for axialturbomachines, many shortcomings remain.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a section through an axial turbomachine in accordance withthe present application.

FIG. 2 shows an axial turbomachine compressor in accordance with thepresent application.

FIG. 3 shows a simplified view of a compressor stator section accordingto the present application.

FIG. 4 shows a stator manufacturing step in a first implementationprocess of the present application.

FIG. 5 shows a first stator manufacturing step in a secondimplementation process of the present application.

FIG. 6 shows a second stator manufacturing step in a secondimplementation process of the present application.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present application aims to solve at least one of the problemspresented by the prior art. More particularly, the present applicationaims to lighten the turbomachine. More particularly, the presentapplication aims to make the turbomachine more compact. The presentapplication also aims to improve the performance of the engine and moreparticularly its compressor.

The present application relates to a stator of an axial turbomachinecomprising an external shell with an annular array of openings and atleast one internal annular groove designed to hold an annular layer ofabradable material, a row of stator blades with platforms located in theopenings and fixed by one or more weld beads between the platforms andthe openings, wherein the row of openings and the internal groovepartially overlap so that part of the weld bead(s) is/are positionedaxially in the internal groove.

According to an advantageous embodiment of the present application, theblade platforms form a lip defining the internal groove.

According to another advantageous embodiment of the present application,the platforms extend over a portion of the bottom of the internalgroove.

According to yet another advantageous embodiment of the presentapplication, the openings pass through the shell and the groove.

According to yet another advantageous embodiment of the presentapplication, the platforms have the general shape of a parallelogram,preferably rectangular, with an upstream side and a downstream side,that part of the weld bead(s) positioned axially in the internal grooveextending along one of the upstream and downstream sides of theparallelogram.

According to yet another advantageous embodiment of the presentapplication, the openings extend along a main direction predominantlyoriented along the stator axis, the said main direction preferentiallyforming an angle less than about 45°, more preferably less than about30° even more preferably less than about 15° with the said axis.

According to yet another advantageous embodiment of the presentapplication, the external shell preferably comprises a single-piececircular wall with a first section comprising the internal groove and asecond section comprising the row of openings and blades, the said wallforming a shoulder between the said sections.

According to yet another advantageous embodiment of the presentapplication, the platforms have surfaces additional to the openings.

According to yet another advantageous embodiment of the presentapplication, the external shell and/or the stator blade platforms have agenerally constant thickness.

According to yet another advantageous embodiment of the presentapplication, the blade platforms are essentially embedded in theopenings of the external shell.

According to yet another advantageous embodiment of the presentapplication, the section of the internal groove extends along a maindirection substantially corresponding to the stator axis, and has asubstantially constant depth greater than about 1.00 mm, preferablygreater than about 2.00 mm, even more preferably greater than about 3.00mm.

According to yet another advantageous embodiment of the presentapplication, the internal annular groove has two shoulders, with atleast one of the two shoulders inclined with respect to theperpendicular to the bottom of the internal annular groove.

According to yet another advantageous embodiment of the presentapplication, the stator has blades attached to the external shell bymeans other than welding.

According to yet another advantageous embodiment of the presentapplication, the stator is a compressor stator, preferably alow-pressure compressor.

By low-pressure compressor is meant a compressor arranged downstream ofthe turbofan. Its inlet pressure is similar to the atmospheric pressureat altitudes encountered during aircraft manoeuvres.

According to yet another advantageous embodiment of the presentapplication, the internal annular groove has a length greater than about5.00 mm, preferably greater than about 10.00 mm, preferably greater thanabout 20.00 mm. This length is measured along the stator axis.

According to yet another advantageous embodiment of the presentapplication, the materials of at least one platform and of the shell aregrades of alloy substantially similar or compatible for being welded toeach other.

According to yet another advantageous embodiment of the presentapplication, the shell has two internal annular grooves, one beinglocated upstream and the other downstream of the openings, the firstpart of the weld bead(s) being located in the upstream groove and asecond part of the weld bead(s) being located in the downstream groove.

According to yet another advantageous embodiment of the presentapplication, the platforms have a thickness greater than that of theexternal shell at the openings.

According to yet another advantageous embodiment of the presentapplication, the weld has a break in the weld on the edges of theannular groove in the external shell

According to yet another advantageous embodiment of the presentapplication, the platform has a portion extending along the outersurface of the external shell and which is welded to the said faceaxially in the internal groove.

The present application also relates to a turbomachine comprising atleast one compressor with at least one stator and at least a turbinewith at least one stator, wherein the or at least one of the compressorand/or turbine stators is in accordance with the present application.

The present application also relates to a method of manufacturing astator in accordance with the present application, comprising thefollowing steps: (a) provision of the external shell and blades, (b)locating and welding the platforms in the openings of the externalshell, and (c) fixing the layer of abradable material in the internalgroove.

According to an advantageous embodiment of the present application, themethod comprises the following stage, preferably between steps (b) and(c): machining the internal surface of the shell to form the internalgroove.

The present application can shorten a turbomachine acting as acompressor. Each stator stage combined with a strip of abradablematerial saves a few millimetres. One centimetre can be saved across thewhole of a low-pressure compressor.

The present application also provides an aerodynamic advantage since thewelds on the stream side are covered by the abradable material. Indeed,some of the irregularities that the welds have in the stream are nowcovered by the abradable material. This is achieved by means of anextension of the weld, as well as constructing a platform and anexternal shell with a step.

The present application facilitates the design of a turbomachine anddoes not require there to be unused spaces between the fixed and movingblade rows. If necessary, these rows can be moved closer to each otherin order to improve flow management and thus optimize engineperformance.

The manufacture of such a stator is facilitated. Accessibility to thewelds is improved because in places they are distanced from the blades,and located in an open throat. The dimensions of the groove enable weldsto be made which cause some rise in temperature.

In the following description, the terms interior and exterior refer to aposition relative to the axis of rotation of an axial turbomachine. Thesame applies to the terms internal and external. Lengths are measuredalong the axis of rotation of the turbomachine, heights radially andwidths at right angles to the heights.

FIG. 1 shows an axial turbomachine. In this case it is a double-flowturbojet. The turbojet 2 comprises a first compression stage, aso-called low-pressure compressor 8, a second compression stage, aso-called high-pressure compressor 10, a combustion chamber 12 and oneor more turbine stages 14. In operation, the mechanical power of theturbine 14 is transmitted through the central shaft to the rotor 4 anddrives the two compressors 8 and 10. Reduction mechanisms may increasethe speed of rotation transmitted to the compressors. Further,different, turbine stages can be connected to the compressor stagesthrough concentric shafts. These latter comprise several rotor bladerows associated with stator blade rows. The rotation of the rotor thusgenerates a flow of air and progressively compresses it up to the inletof the combustion chamber 12. An inlet fan commonly called a turbofan 6is coupled to the rotor 4 and generates an airflow which is divided intoa primary flow 16 passing through the different stages of theturbomachine mentioned above and a secondary flow 18 passing through anannular passage (shown in part) running the length of the machine whichthen rejoins the main flow at the turbine outlet.

FIG. 2 is a sectional view of a low-pressure compressor of an axialturbomachine such as that in FIG. 1. The diagram shows a portion of theinlet fan or turbofan 6 and the flow splitter nose 20 separating theprimary flow 16 and the secondary flow 18. The rotor 4 includes severalrows of rotor blades 22. The housing comprises several stators 24associated with rotor blade rows 22. Each stator comprises a row ofstator blades 26. Each pair of rotor and associated stator blade rowsforms one compressor stage of the compressor 8.

FIG. 3 illustrates part of the stator 24 of the turbomachine. The stator24 forms a ring having as its axis the axis of symmetry of rotation ofthe turbomachine. It comprises an external shell 28 in which a statorblade 26 is fixed. The external shell 28 has an internal surface tochannel the primary flow. Its internal surface is a surface ofrevolution. It is substantially cylindrical and shows a variation indiameter, for example a reduction in diameter in the direction of flow.The shell has a body of revolution developed from a profile ofrevolution. The profile of revolution has a first part 30 and a secondpart 32 connected by a curved region 34. The first part 30 and thesecond part 32 can be interleaved at the curved region 34.

The first part 30 may be an upstream portion. It has an internal annulargroove in which there is an annular layer 36 of abradable material. Thismaterial is able to be eroded by friction when a rotor blade tip 22comes into contact with it. The layer of abradable material 36 may forman annular band of substantially constant thickness, in order tostreamline and simplify its implementation. The internal surface of thelayer of abradable material 36 is flush with the internal surface of theplatform of the stator blade 26. This configuration optimises the flowand creates no surface discontinuity to disrupt the flow.

The length of the layer of abradable material 36 is dictated by thelength of the tip of the rotor blade 22 opposite it. Upstream anddownstream borders can be added to this length to take turbomachineservice variations into account. These lengths are measured along theaxis of rotation of the turbomachine. The length of the layer ofabradable material 36 may be considered as a fixed datum of theturbomachine's geometry.

The second part 32 may be a downstream portion. It has an externalannular groove forming an annular recess. This recess will lighten theexternal shell.

The second part 32 has an opening through the external shell 28. Thestator blade has a platform 38 with a surface matching the opening so asto mask the latter. The platform 38 is fixed at its junction with theopening, preferably at its edges, preferably along its entire margin.

Fixing is carried out by welding, preferably by seam welding, preferablycontinuously. The weld bead is formed over the entire periphery of theopening so as to create a seal. Welding forms a weld bead with anupstream part 40 and a downstream part 42, and side parts (not shown).This weld can be achieved by electron beam welding.

Advantageously, the second part 32 comprises a row of openings holding arow of stator blade platforms. Preferably, the external edges of theplatform 38 extend the length of the internal edges of the openings.Preferably, the openings are similarly shaped to the platforms 38.

The upstream part of the weld 40 is located under the layer of abradablematerial 36. At this location, the shape of the body of the externalshell 28 is substantially straight. The upstream part of the weld 40 ispositioned so as to overcome any geometric constraints. The position ofthe weld can no longer be located between the curved region 34 and thebody of the stator blade. Thus, the constraints imposed to extend theplatform between the curved region 34 and the blade body no longerexist. In addition, the length of the upstream portion of the weld 40 isless than the length of the layer of abradable material 36 and thepresence of the upstream part 40 of the weld no longer affects thelength of the external shell 28.

Thus, compared to a stator known by prior art, that part of the platformbetween the stator blade body and the curved region 34 can be shortened.This reduction in axial length affects the external shell 28. For this,all the welded stator blades on one stage must have their upstream part40 of their welds arranged in the same groove. A substantial reductionin length can be achieved at each upstream or downstream weld locatedunder a layer of abradable material 28. This reduction can be greaterthan about 2.00 mm, preferably greater than about 3.00 mm. Over acompressor comprising several stages of compression, for example, threestages of compression, the present application might yield a reductionof more than about 10.00 mm. The engine housing can also be shortened.These reductions enable the turbomachine to be both lightened and madestronger.

The teachings of the present application can also be applied to aturbomachine turbine stator. A weld on a stator blade platform can beshifted axially so as to remove it from a region having constraints.Thus, a significant reduction in length can be attained by applying theteachings of the present application to both the turbomachine'scompressor(s) and turbine(s). In this case, the abradable material maybe a material with a honeycomb structure.

Various processes enable the stator 24 to be implemented.

FIG. 4 shows an intermediate stator 24 implementation step in a firstfabrication process. The stator 24 is formed from an external shell withopenings in which the platforms are housed. The shell 28 and theplatforms 38 show their finished dimensions.

A weld bead is made at the junction between the platforms and theopenings of the external shell. The weld bead is basically thin, itsthickness being close to that of the external shell 28. It is cheap toproduce due to its small cross section. A thickened portion 44 can beadded at the platform in the curved region 34. After welding, thethickened portion 44 is machined, for example by turning.

The first method for fabricating the stator comprises the followingsteps:

manufacture the external shell 28 and the blades 26 to their finisheddimensions;

locate and weld the platforms 38 in the openings of the external shell28 so that they are flush with the internal surfaces; and

weld the platforms 38 to the openings in the external shell.

FIG. 5 shows a first intermediate step in the manufacture of the stator24 shown in FIG. 3. FIG. 5 has the same numbering scheme as in previousfigures for the same or similar elements, but the numbering isincremented by 100. Specific numbers are used for items specific to thisembodiment.

In this process, the stator is made from rough-finish platforms 138 anda rough-finish blade 126 with a rough-finish external shell 128 havingradially thickened portions. They may have equal thicknesses where theyjoin. The rough-finish platforms 138 and the rough-finish blades 126 arefitted into the openings of the rough-finish external shell 128 and arethen welded at their junctions. FIG. 5 illustrates a rough-finishupstream part 140 and a rough-finish downstream part 142 of the weldbead. The assembly thus obtained is a rough-finish stator 124.

FIG. 6 shows a second intermediate stage of the second statormanufacturing process. The second intermediate step includes machiningoperations on the rough-finish stator shown in FIG. 5. The machiningoperations may include rough and/or final machining.

An internal machining pass 102 is carried out on the internal surface ofthe rough-finish stator 124. It creates an annular groove into which alayer of abradable material may be deposited. Several annular groovesarranged axially can be made to accommodate several annular layers ofabradable material. The internal machining 102 extends axially on therough-finish external shell 128 and on part of the rough-finishplatforms 138. It also removes material from the upstream portion 102 ofthe weld bead.

One or more external machining passes 104 may be carried out on theouter surface of the rough-finish stator 124. These machining passesenable the stator to be lightened by removing material. Such machiningpasses can be performed on the rough-finish stator blade platforms 138as well as in the downstream part 142 of the weld bead.

The internal and/or external machining passes are advantageously carriedout by turning to improve their circularity and cylindricity.

The second method for fabricating the stator comprises the followingsteps:

manufacture the rough-finish external shell 128 and the rough-finishblades 126 and the rough-finish platforms 138;

locate and weld the rough-finish platforms 138 in the openings of theexternal rough-finish shell 128;

carry out internal machining 102 on the internal face of therough-finish external shell 128, carry out external machining 104 of theexternal face of the rough-finish external shell 128; and

fit the layer of abradable material in the internal groove.

The second manufacturing process has the advantage of welding on a flatsurface. This weld will be more homogeneous and therefore more durable.In addition, welding can change the crystal structure of materials andmake them more brittle. This embrittlement, combined with a curvedregion, can shorten the life of the piece so formed. Thermal andvibratory stress may precipitate mechanical failure. By locating a weldunder the strip of abradable material, away from the curved region, theshell becomes more durable.

1. An axial turbomachine stator, comprising: an external shell having an annular array of openings and at least one annular internal groove configured to receive an annular layer of abradable material; and a row of stator blades having platforms located in the openings and secured by one or more weld beads between the platforms and the openings; wherein the row of openings and the internal groove partially overlap so that a part of each weld bead is positioned axially in the internal groove.
 2. The stator according to claim 1, wherein the platforms of the blades form a lip defining the internal groove.
 3. The stator according to claim 1, wherein the platforms extend over a portion of the bottom of the internal groove.
 4. The stator according to claim 1, wherein the openings pass through the shell and the internal groove.
 5. The stator according to claim 1, wherein the platforms have the general shape of a parallelogram, with an upstream side and a downstream side, the part of each weld bead being positioned axially in the internal groove and extending along one of the upstream and downstream sides of the parallelogram.
 6. The stator according to claim 1, wherein the platforms have the general shape of a rectangular, with an upstream side and a downstream side, the part of each weld bead positioned axially in the internal groove extend along one of the upstream and downstream sides of the parallelogram.
 7. The stator according to claim 1, wherein the openings extend along a main direction predominantly oriented along the axis of the stator, the said main direction forming an angle less than about 45° with the said axis.
 8. The stator according to claim 1, wherein the openings extend along a main direction predominantly oriented along the axis of the stator, the said main direction forming an angle less than about 30° with the said axis.
 9. The stator according to claim 1, wherein the openings extend along a main direction predominantly oriented along the axis of the stator, the said main direction forming an angle less than about 15° with the said axis.
 10. The stator according to claim 1, wherein the external shell comprises: a single-piece circular wall having a first section comprising the internal groove and a second section comprising the row of openings and blades, the wall forming a shoulder between the first section and the second section.
 11. The stator according to claim 1, wherein the platforms have surfaces additional to the openings.
 12. The stator according to claim 1, wherein at least one of either the external shell of the stator blades or the platforms is generally of constant thickness.
 13. The stator according to claim 1, wherein the platforms of the blades are substantially embedded in the openings of the external shell.
 14. The stator according to claim 1, wherein the internal section of the groove extends in a main direction corresponding substantially to the axis of the stator, and has a substantially constant depth greater than about 1.00 mm.
 15. The stator according to claim 1, wherein the internal section of the groove extends in a main direction corresponding substantially to the axis of the stator, and has a substantially constant depth greater than about 2.00 mm.
 16. The stator according to claim 1, wherein the internal section of the groove extends in a main direction corresponding substantially to the axis of the stator, and has a substantially constant depth greater than about 3.00 mm.
 17. The stator according to claim 1, wherein the internal annular groove comprises two shoulders, at least one of the two shoulders being inclined relative to the perpendicular to the bottom of the internal annular groove.
 18. A turbomachine, comprising: at least one compressor having at least one stator; and at least one turbine having at least one stator; wherein at least one of the compressor stator or the turbine stator, comprises: an external shell with an annular array of openings and at least one internal annular groove designed to hold an annular layer of abradable material; and a row of stator blades with platforms located in the openings and secured by one or more weld beads between the platforms and the openings; wherein the row of openings and the internal groove partially overlap so that a part of each weld bead is positioned axially in the internal groove.
 19. A method of manufacturing a stator, comprising: providing an external shell and blades, the external shell having an internal groove for receiving abradable material; locating and welding platforms in the openings of the external shell; and fitting a layer of abradable material in the internal groove.
 20. The method according to claim 19, wherein the internal groove is formed by machining an inner surface of the external shell. 